The Reddit AMA was a little vague. Suzuki-san stated that Shenmue has 11 chapters, but it was originally meant to be 16, and we already know of at least one cut chapter (on the boat to China). He could've meant there are 11 chapters remaining, and given that Shenmue II had 4 I don't see how all 11 would fit into one game.
I just hope we get to see the story finished. If Shenmue III doesn't end the tale and we never get Shenmue IV then we're no better off really. Perhaps he will develop III and IV at the same time and release them a year apart.....